You do it yourself mate. You can put on and take off the map at any time. Its not cheap though. There figures quote 204 bhp, but every member with a BSR map that's had it on the rollers has easily surpassed that on a otherwise stock car.
http://www.bsruk.co.uk/index.html
Uk distributor is LMF
http://www.lmfvauxhall.co.uk/store/prod ... t=0&page=2
One lad has just has a TMS superchip map put on his but it failed. There are other systems like the BSR out there like Regals unit, but from what i'm aware the BSR one is the only real one to go for.
Do a search over on vec c for BSR, there are tonnes of thread all full of praise mate.